How to design an AI that discovers more complex concepts on its own?
This is not an answer. I couldn't comment, so here are some remarks about your question: This is a very broad question, and considered The Holy Grail for building artificially intelligent systems - meaning that some scientists have been dreaming about this since time immemorial. 

Some homework is warranted from your side; you could have offered some of your solutions or maybe identified the multiple layers to your query, as they invoke concepts from many fields within the study of AI (or AGI to be general).  

For example, the following layers are taken up around the big-words in the question, though rhetorically - 


On evolution - what registers as evolution (is only genetic mutation evolution or should it involve some form of natural selection or seeking a niche for increasing the chances of survival or etc). How would evolution of software look like? Should it be able to modify its own code in the process of evolution? 
On concept - what constitutes a concept, identifying from the environment a concept by calculating its relevance (w.r.t other concepts), coming with a process of selecting the concept for use in a given environment (natural or artificial).Referring to the example in the question, is the road a relevant concept or the trees and the sky and the bees pollinating some flowers along the roadside? What is a more fundamental concept - the trees or the bees, and how does one measure that?
On rewards - for us humans, rewards are maximization of survival of genetic machinery they carry (translating to reproductive success). what reward system should we come up that machines could use to increase their chances of survival in the physical world? what value should be put on a reward for moving the car on a straight line, or moving from darkness towards light? Shouldn't moving from darkness to light be more fundamental action (concept) and therefore rewarded higher than moving along the straight line? However, given that the car has learned to move from darkness to light, shouldn't the value of the reward be lowered so that it can learn other actions/concepts?


As can be seen from this brief detailing, there are layers within layers. Therefore, it is proper to establish now that there are no simple answer to this essay-requiring soul-searching time-eating heavy-research-wanting question. However appropriate directions can be given about work that is being done by some of the most prominent scientists of our times. The thing that one is looking for are known as Universal Problems Solvers, such as Gödel Machine (by Jürgen Schmidhuber) and AIXI - Artificial Intelligence (AI) based on Solomonoff's distribution ξ (by Markus Hutter). 

Here is a quote lifted from Wikipedia page on AIXI that is pretty self-explanatory on how it maximizes the rewards over time.  


  AIXI is a reinforcement learning agent. It maximizes the expected
  total rewards received from the environment. Intuitively, it
  simultaneously considers every computable hypothesis (or environment).
  In each time step, it looks at every possible program and evaluates
  how many rewards that program generates depending on the next action
  taken. The promised rewards are then weighted by the subjective belief
  that this program constitutes the true environment. This belief is
  computed from the length of the program: longer programs are
  considered less likely, in line with Occam's razor. AIXI then selects
  the action that has the highest expected total reward in the weighted
  sum of all these programs.


Gödel Machine goes further - it allows the agent to modify its own code that allows it to maximise the rewards of its actions - which is to modify its own code that allows it to maximize the rewards of its actions - as so on. This is kind of a recursive definition, that simulates evolution (a rapid one) by choosing to evolve that code/state of the agent that converges towards a code that is superior to the code that the agent is currently running.

Here is a quote lifted from page on summary of Gödel machine. See that Hutter is also referenced (discovered of AIXI above). 


  Our Gödel machine will never get worse than its initial problem
  solving strategy, and has a chance of getting much better, provided
  the nature of the given problem allows for a provably useful rewrite
  of the initial strategy, or of the proof searcher. The Gödel machine
  may be viewed as a self-referential universal problem solver that can
  formally talk about itself, in particular about its performance. It
  may "step outside of itself" (Hofstadter, 1979) by rewriting its
  axioms and utility function or augmenting its hardware, provided this
  is provably useful. Its conceptual simplicity notwithstanding, the
  Gödel machine explicitly addresses the `Grand Problem of Artificial
  Intelligence' by optimally dealing with limited resources in general
  environments, and with the possibly huge (but constant) slowdowns
  buried by previous approaches (Hutter, 2001, 2002) in the widely used
  but sometimes misleading O()-notation of theoretical computer science.
  
  The main limitation of the Gödel machine is that it cannot profit from
  self-improvements whose usefulness it cannot prove in time.


Reading the papers of the stated research would certainly be useful in finding answers to some of the layers in the question. There is also good work going on in the AGI community that somewhat aligns with the direction. Hope this helps.